San Lorenzo Valley Water District weighs CZU complex fire rebuild options

San Lorenzo Valley Water District Manager Rick Rogers holds a small piece of the seven miles of polyethylene pipeline burned during the CZU Lightning Complex. (Melissa Hartman - Santa Cruz Sentinel) — San Lorenzo Valley Water District Manager Rick Rogers holds a small piece of the seven miles of polyethylene pipeline burned during the CZU Lightning Complex. (Melissa Hartman – Santa Cruz Sentinel)

PUBLISHED: March 16, 2022 at 4:20 p.m. | UPDATED: March 16, 2022 at 6:35 p.m.

FELTON – The San Lorenzo Valley Water District could decide Thursday just how it will rebuild some 7 miles of scorched drinking water pipeline – which burned in the August 2020 CZU Lightning Complex fire.

The flexible, yet thick high-density polyethylene pipeline didn’t fare well in the historic blaze. The plastic pipe wound through steep Santa Cruz Mountains topography, and sat above ground, which made it particularly vulnerable to wildfire. As a result, the district lost nearly all of its surface water sources, forcing the purveyor to rely on the Santa Margarita Groundwater Basin to provide drinking water — an aquifer that is critically overdraft, meaning more water has been pulled out of the aquifer than replenished over the years.

The CZU Complex damage also meant district customers were without tap water for weeks to months. The purveyor proactively shut down its treatment plant – preventing long-lasting contamination from entering the system. Officials found elevated levels of volatile organic compounds such as benzene in parts of the water supply directly after the blaze, though contamination has since diminished to state-standard levels.

Trees that line a road up leading to a San Lorenzo Valley Water District water treatment plant are blackened from the CZU Complex fire. (Melissa Hartman – Santa Cruz Sentinel)

Still, risks to drinking water supply due to wildfire, earthquakes and debris flows – fast-moving slurries of rock, soil and sediment carried in water – remain a threat. Now, the district’s board of directors could greenlight how the purveyor chooses to recover from the CZU Complex fire, and if it will be more resilient to future disasters.

The San Lorenzo Valley Water District hired San Mateo-based Freyer & Laureta Inc., a consultant whom – with the district’s engineering team – analyzed rebuild options. The district considered rerouting the pipeline – one option included rebuilding it along Highway 9 – and reconstructing it with steel or iron, as opposed to HDPE. The consultants also analyzed various depths at which the pipe could be susceptible to fire.

According to San Lorenzo Valley Water District General Manager Rick Rogers, the most protective, cost effective rebuild option is to bury the 7 miles of pipeline 2 feet below the surface.

“The depth of 2 feet of cover over the pipe is a very comfortable backfill to protect from fire … that would protect the pipe from another CZU fire if it came through,” Rogers said.

Burying the HDPE pipe could add a layer of protection from large-scale damage and contamination, should another historic wildfire erupt in the Santa Cruz Mountains. But even if during Thursday’s board meeting, representatives vote to rebuild the system under a layer of dirt, financial, environmental, construction and regulatory hurdles remain.

“This is like cutting a single lane roadway and then burying the pipe 2 feet,” said San Lorenzo Valley Water District General Manager Rick Rogers. “It’s a huge deal, it’s a huge project with a $60 million price tag.”

The pipeline, built some 20 years ago, previously ran along a 4 to 6 foot wide hand cut trail along the remote stretches of Empire Grade Mountain. Construction of a new, upgraded buried pipeline could also provide emergency access to the rural area, said Rogers.

“Could there be some additional benefits by making this trail that will be much more substantial than what’s there now – could this trail be used for future firefighting and access to, to the Empire Grade Mountain, for Cal Fire?”

But to build the pipeline below ground, comes the necessity of serious excavation, trenching, construction of retaining walls and forest thinning.

Science emerging

Purdue University Professor of Civil, Environmental and Ecological Engineering Andrew Whelton said though the science is still emerging, anecdotal evidence shows buried pipes in general withstand wildfire better.

“There is evidence that if you bury pipes, it should reduce the potential damage to that pipe should a fire be present on the surface,” Whelton said.

Fire burns through the water district’s polyethylene piping during the CZU Lightning Complex Fire, leaving a molten black exterior in its wake. (Courtesy of the San Lorenzo Valley Water District)

What depth the pipe must be buried to largely depends on a region’s soil type, how readily the dirt transfers heat and what material is burning – grass, logs, or otherwise, Whelton said.

In the wake of devastating large-scale wildfires, such as the Camp fire in Paradise, researchers and officials have just recently begun to investigate how water infrastructure can be made more resilient.

“The consideration of wildfires in the design of public water systems is just one consideration of many for climate change,” said Oregon State University Civil and Construction Engineering Assistant Professor Erica Fischer. “I think it is a relatively new arena.”

Wildfire risk to water infrastructure can also be further reduced by thinning forest and overgrown vegetation, Fischer said, who’s currently working on a survey that aims to document how water districts are choosing to build back in the wake of wildfires.

“I believe when the public is engaged in the recovery process, there is a lot more trust in their local government, and they feel like they have more stake in the game of recovery,” Fischer said, adding that water districts should make “strategic decisions based on how much the public wants to spend.”

First step

The San Lorenzo Valley Water District is facing hefty costs to rebuild its system, along with a general downward trend in water sales, according to Rogers. The purveyor went over its 2021 fiscal year budget — to the tune of $1 million in expenses — largely to fund initial fire recovery projects.

While a rate increase and a special CZU Complex recovery charge went into effect in the last year, the district is still facing financial challenges. What remains to be seen is how long those challenges last, Rogers said.

And, even if the board votes to move forward with burying the pipe, the decision is just a first step to move towards what will be a multi-year project.

Rogers also said that while the burying measure would insulate the infrastructure from wildfire, the pipeline may still be susceptible to impacts from strong storms.

“We may be able to harden against fire that comes through, but we do know we receive storm events that happen every year — we’re concerned about erosion and drainage issues due to that,” Rogers said.

That potential maintenance would likely mean another new cost for the district. Rebuilding the pipeline above ground, in its same place – and still susceptible to wildfire – remains an option on the table, according to Rogers.